1. Field of the Invention
This invention relates to oil-in-water emulsions (hereinafter referred to as O/W-emulsions) and, more particularly, to topical, cosmetic and pharmaceutical preparations in the form of an O/W-emulsion.
2. Statement of Related Art
The viscosity and rheological behavior of O/W-emulsions are determined on the one hand by the nature, quantity and fineness of the disperse phase and, on the other hand, by the composition of the continuous aqueous phase. In the case of emulsions intended for the care of hard surfaces or for dermatocosmetic, trichocosmetic, or pharmaceutical topical applications, rheological behavior has a considerable bearing on the subjective feeling on application.
Emulsions for cosmetic application to the skin are expected by the user to create a nourishing feeling when rubbed onto the skin. However, any increase in the proportion of oil phase often leads to an undesirable greasy feeling on the skin.
For this reason, water-soluble polymers, specifically hydrocolloids, have been added to the aqueous phase in order to control its viscosity. In the case of cosmetic and pharmaceutical topical O/W-emulsions, it is known to use water-soluble vegetable gums, such as alginates and tragacanth, water-soluble cellulose derivatives, such as carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, water-soluble starch derivatives and synthetic polymers, such as polyvinylalcohol, polyethylene oxides or polyacrylic acids, in order to thicken the aqueous phase and to stabilize the emulsions.
Aqueous solutions of these polymers, like solutions of most water-soluble polymers, show structural viscosity, in other words their viscosity decreases under the effect of shear forces. O/W-emulsions of which the aqueous phase is thickened by structurally viscous polymers such as these are attended by the disadvantage that, when the emulsion is rubbed onto the skin, there is little of the viscosity to be felt on account of the shear forces generated during rubbing, so that the emulsions lack substance and have little cosmetic appeal.